KR20050051106A - Polyethylene-2,6- naphthalate fibers by high speed spinning - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polyethylene naphthalate fiber by a high-speed spinning method in which the strength of stretched yarn is improved by adjusting the fineness and the force-strain curve of the partially oriented yarn (POY), and polyethylene-2,6-naphthalate having an intrinsic viscosity of 0.80 to 1.2. The chip is melt-extruded through a spinneret, passed through a suitable heating section under the spinneret, and then cooled and solidified using a cooling gas to prepare POY yarn. The single yarn fineness of the POY yarn is 4 to 10 denier, and 0.5g at room temperature. winding yarn at a radial velocity such that the birefringence is 0.02 to 0.20 when the initial stress of / d is less than 5%, and the wound yarn is not more than 2.5 times the total draw ratio It relates to a high strength polyethylene-2,6-naphthalate yarn prepared by a method comprising the step of stretching in multiple stages.

In addition, the polyethylene-2,6-naphthalate industrial yarn of the present invention has a high spinning speed and high productivity, which is advantageous in terms of economy, and the dip cord manufactured therefrom provides excellent strength utilization and adhesion.

Description

Polyethylene-2,6-naphthalate fibers by high speed spinning

The present invention relates to a polyethylene naphthalate fiber that improves the strength of stretched yarn by adjusting the fineness and force-strain curve of the partially oriented yarn (POY), the polyethylene-2,6-naphthalate industrial yarn of the present invention has a high spinning speed The productivity is high and economically advantageous, and the deep cord manufactured therefrom provides excellent strength utilization and adhesion.

Polyethylene-2,6-naphthalate has a bulky naphthalate unit, which has a higher glass transition temperature, crystallization temperature, melting temperature, and melt viscosity than polyethylene terephthalate. That is, in order to lower the melt viscosity of the melt during spinning has been spun at a relatively higher temperature than the normal spinning temperature (310 to 320 ℃).

However, spinning at high temperatures can lead to pyrolysis of the melt, resulting in poor stretchability and a significant decrease in intrinsic viscosity, so that high strength yarns can be used with polyethylene-2,6-naphthalate polymers. ) Was difficult (see Japanese Patent Laid-Open Nos. 47-35318, 48-64222, and 50-50739).

Thus, Japanese Patent No. 2945130 manufactures high strength and high modulus polyethylene-2,6-naphthalate fibers by adjusting the spinning speed and spinning draft ratio instead of increasing the spinning temperature and adjusting the stretching temperature step by step. A method of doing this is disclosed. According to this method, however, not only uniform spinning is difficult but also the temperature of the first stage stretching exceeds 150 ° C., resulting in a wider width, which makes it difficult to normalize stretching.

US Pat. No. 4,101,525 (Davis et al.) And US Pat. No. 4,491,657 (Cyto et al.) Disclose industrial polyester multifilament yarns having high initial modulus and low shrinkage. However, it is known that the yarns disclosed in these patents do not satisfy the characteristics required as tire cords due to a decrease in strength when converted into treatment cords.

Therefore, as a method of increasing the strength of multifilament polyester fibers, US Patent No. 4,690,866 proposes a method of spinning using polyester chips having a high intrinsic viscosity (I.V.) of 1.2 or more. Increasing the viscosity of the chip increases the orientation of the unstretched yarn and increases the formation of a tie chain that connects the crystal to the crystal, thereby exhibiting excellent strength when converted to the treatment cord. However, the high intrinsic viscosity used in this method is very different from the intrinsic viscosity of the surface and the central part during solid state polymerization, so when melt spinning, the radioactivity is lowered due to the viscosity unevenness and filament cut is generated, resulting in fairness and appearance. In addition to being poor, since the thermal radiation and hydrolysis occurs due to the melt spinning at a high temperature, the fibers that are actually spun have a problem that does not have a high viscosity as the chip has.

When manufacturing industrial polyester yarns, the strength of the final stretched yarn can be increased only by increasing the radial tension to increase the orientation of the partially aligned yarn (POY) and the formation of a tie chain connecting the crystals with the crystals. In order to obtain a high-strength stretched yarn, it is necessary to obtain a POY microstructure capable of stretching at high magnification.

In this regard, the present invention increases the formation of a tie chain that connects crystals with the orientation and orientation of the partial alignment yarns (POY) by controlling the fineness and force-strain curve of the partial alignment yarns (POY). Could increase the strength of the drawer.

The present invention relates to a high-strength polyethylene naphthalate fiber in which fineness and force-strain curves of partial alignment yarns (POY) are adjusted, and POY has a single yarn fineness of 4 to 10 deniers, and an initial stress of 0.5 g / d at room temperature. Tie chains that connect the crystals with the orientation and crystallization of the partial alignment yarn (POY) in the drawing phase by winding yarns at radial speeds with a force strain curve that stretches less than 5% when faced and a birefringence of 0.02 to 0.20 It is an object of the present invention to provide a polyethylene-2,6-naphthalate fiber and a method of manufacturing the same by maximizing the formation of (tie chain) by a high-speed spinning method excellent in physical properties.

In addition, the polyethylene-2,6-naphthalate industrial yarn of the present invention has a high spinning speed and high productivity, which is advantageous in terms of economy, and the dip cord manufactured therefrom provides excellent strength utilization and adhesion.

The present invention (A) extruded a polymer containing not less than 85 mol% of ethylene naphthalate units and having an intrinsic viscosity in the range of 0.80 to 1.2 at a temperature of 290 to 330 ° C., and then quenching the melt-release yarn through a delayed cooling zone. Solidifying step (B) at room temperature, the partial orientation yarn has a single strain fineness of 4 to 10 deniers and a force strain curve that is less than 5% when subjected to an initial stress of 0.5 g / d, and an initial of 10 to 50 g / d Modulus, winding the yarn at a spinning speed such that the birefringence is 0.02 to 0.20, (C) multi-stretching the wound yarn at a total draw ratio of 2.5 times or less, It provides a polyethylene naphthalate fiber having.

(1) intrinsic viscosity of 0.6 to 1.0, (2) strength of 8.0 g / d or more, (3) elongation of 6% or more, (4) 2 to 4 denier of single yarn fineness, (5) 1000 to 2000 denier of total fineness, (6) shrinkage of 1 to 4%

It is also preferable that the total fineness of the stretched yarn is 1500 denier and the number of filaments is 500.

It is also preferable that the total fineness of the stretched yarn is 1500 denier and the number of filaments is 385.

Further, in step (A), it is preferable to install a heating zone adjacent to just before the cooling zone and having an ambient temperature of 300 to 400 ° C. and a length of 200 to 700 mm.

In addition, the spinning speed in the step (B) is preferably 2,000 to 3,500 m / min.

The present invention provides a deep cord obtained by treating two strands of polyethylene naphthalate fibers up and down and treating with resorcinol-formalin-latex (RFL).

In addition, it is preferable that the strong utilization rate of the deep code is 85%.

In addition, it is preferable that the adhesive strength of the deep cord is 10kg or more.

The present invention provides a rubber product in which a deep cord is incorporated as a reinforcing material.

The polyethylene-2,6-naphthalate polymer used in the present invention contains at least 85 mole% of ethylene-2,6-naphthalate units and preferably consists only of ethylene-2,6-naphthalate units.

Optionally, the polyethylene-2,6-naphthalate may incorporate as a copolymer unit a small amount of units derived from one or more ester-forming components other than ethylene glycol and 2,6-naphthalene dicarboxylic acid or derivatives thereof. Can be. Examples of other ester forming components copolymerizable with polyethylene naphthalate units include glycols such as 1,3-propanediol, 1,4-butanediol, 1,6-hexanediol, and the like, terephthalic acid, isophthalic acid, hexahydroterephthalic acid, stilbene Dicarboxylic acids such as dicarboxylic acid, bibenzoic acid, adipic acid, sebacic acid, azelaic acid.

Polyethylene naphthalate chip according to the present invention, preferably naphthalene-2,6-dimethylcarboxylate (NDC) or naphthalene-2,6-dimethylcarboxylic acid (NDA) and ethylene glycol raw material in a ratio of 2.0 to 2.3 Melt mixed at 190 ° C., and the melt mixture was subjected to transesterification (for about 2 to 3 hours at 220 to 230 ° C.) and condensation polymerization (for about 2 to 3 hours at 280 to 290 ° C.) to 0.42 to After making a raw chip of 0.70 level, it is solid-phase polymerized to have an intrinsic viscosity of 0.80 to 1.20 and a moisture content of 30 ppm or less under a temperature of 240 to 260 ° C and a vacuum.

The present invention may optionally add a manganese compound, preferably manganese acetate, in a transesterification reaction in an amount such that the remaining amount of manganese metal in the final polymer is in the range of 30 to 70 ppm, the amount being 30 If it is less than ppm, the transesterification reaction rate becomes too slow, and if it is more than 70 ppm, more manganese metals than necessary will act as foreign matters, causing problems during solid state polymerization and spinning.

In the present invention, optionally, during the polycondensation reaction, as a polymerization catalyst, an antimony compound, preferably antimony trioxide, may be added in an amount such that the amount remaining as an antimony metal in the final polymer is from 180 to 300 ppm. When less, the polymerization reaction rate is lowered and the polymerization efficiency is lowered. When the amount is higher than 300 ppm, more than necessary antimony metal acts as a foreign material, which degrades radio-stretching workability. In this case, a phosphorus heat stabilizer, preferably trimethyl phosphate, may be added in an amount such that the remaining amount of phosphorus element in the final polymer is 35 to 45 ppm, and the manganese / phosphorus content ratio is 2.0 or less. When the manganese / phosphorus content ratio is higher than 2.0, the oxidation is promoted during the solid phase polymerization, so that normal physical properties cannot be obtained during spinning.

The polyethylene naphthalate chip thus produced is fiberized according to the method of the present invention, and FIG. 1 schematically shows a manufacturing process according to one embodiment of this invention.

In step (A), the polyethylene naphthalate chip is passed through the pack 1 and the nozzle 2, preferably at a spinning temperature of 290 to 328 ° C., preferably at a spinning draft ratio of 200 to 800 (on the first take-up roller). Low-temperature melt spinning at a linear velocity / linear velocity) can prevent a decrease in the viscosity of the polymer due to thermal decomposition and hydrolysis. If the draft ratio is less than 200, the uniformity of the filament cross section is worse, the drawing workability is significantly reduced. If the draft ratio exceeds 800, filament breakage occurs during spinning, making it difficult to produce a normal yarn.

In the present invention, it is also an important factor to adjust the filtration residence time in the pack to 3 to 20 seconds. If the filtration residence time in the pack is less than 3 seconds, the filtration effect of the foreign matter is insufficient, and if it is more than 20 seconds, the molecular weight decreases due to excessive pack pressure increase.

In addition, in the present invention, it is preferable to set the L / D (length / diameter) of the extruder screw to 20 to 50, which is difficult to uniformly melt when the L / D of the screw is less than 20, and to exceed 50 due to excessive shear stress. Molecular weight fall is severe and physical property is inferior.

In step (A), the quenching yarn 4 is quenched by passing through the cooling zone 3, if necessary, the distance from the nozzle 2 directly under the nozzle 2 to the starting point of the cooling zone 3, ie the length of the hood ( L) A short heating device may be fitted in the section.

This zone is called delayed cooling zone or heating zone, which has a length of 50 to 250 mm and a temperature of 250 to 400 ° C. (air contact surface temperature).

In the cooling zone 3, an open quenching method, a circular closed quenching method, and a radial outflow quenching method may be applied depending on a method of blowing cooling air. It is not limited to. Subsequently, the discharged yarn 4 solidified while passing through the cooling zone 3 can be oiled by the emulsion applying device 5 to 0.5 to 1.0%.

In step (B), the partial alignment yarn (POY) has a single yarn fineness of 4 to 10 denier, has a force strain curve that is less than 5% when subjected to an initial stress of 0.5 g / d at room temperature, and the birefringence is The yarns are wound at a spinning speed of 0.02 to 0.20, with a preferred spinning speed of 2,000 to 3,500 m / min. If it is less than 2,000 m / min, the partial orientation yarn cannot be induced, and if it exceeds 3,500 m / min, the crystallinity of the partial orientation yarn is high, the elongation is low, and it is difficult to manufacture high strength yarn.

In the present invention, the fineness of the partial alignment yarn POY, the force-strain curve, and the birefringence are used as factors for controlling the microstructure of the partial alignment yarn POY.

As a key technology in the present invention, the single yarn fineness of the partial alignment yarn (POY) is adjusted to be 4 to 10 deniers than the conventional one. In the prior art, the single yarn fineness of the partially oriented yarn (POY) exceeds 10 denier. In this case, the partial oriented yarn (POY) is too thick to have uniform cooling. In other words, due to the cooling difference between the surface and the inside of the partially oriented yarn (POY), damage to the yarn in the stretching process. In addition, when the single yarn fineness of the partial alignment yarns (POY) is 4 denier or less, the number of filaments of the partial alignment yarns (POY) increases, resulting in poor radioactivity.

In the present invention, the partial alignment yarn (POY) is characterized by having a force deformation curve that is less than 5% when subjected to an initial stress of 0.5g / d at room temperature.

The partial orientation yarn (POY) having the force deformation curve can be maximized in the stretching process in a subsequent stretching process.

In addition, in the present invention, the birefringence of the partial alignment yarn (POY) is used as a factor for controlling the microstructure of the undrawn phase together with the force-strain curve.

In particular, in the present invention, as described above, only the partial orientation yarn (POY) fineness, the force strain curve, and the birefringence satisfy all of the above-described ranges, thereby obtaining excellent stretchability in the stretching step. This is because if the birefringence of the partially oriented yarn (POY) is less than 0.02, the crystallization rate is too slow in the stretching step to sufficiently induce the formation of tie chains between the crystals. If the birefringence exceeds 0.20, the crystallization during stretching It progresses so rapidly that it is rather difficult to produce high strength yarns because of its elongation.

In step (D), the yarn having passed through the first drawing roller 6 is passed through a series of drawing rollers 7, 8, 9 and 10 by spin draw method while the total draw ratio is 2.5 times or less, preferably Obtains the final stretched yarn 11 by stretching 1.5 to 2.2 times.

In the present invention, the POY yarn is drawn in two or three stages, and each drawing temperature is higher than POY's glass transition temperature and is 230 ° C. or lower, which indicates that the drawing temperature is lower than the glass transition temperature. It is because when it falls and exceeds 230 degreeC, crystallization advances rapidly during extending | stretching, and it is difficult to carry out two-stage or three-stage stretching.

Stretched polyethylene naphthalate fibers prepared according to the method of the present invention have (1) intrinsic viscosity of 0.6 to 1.0, (2) strength of 8.0 g / d or more, (3) elongation of 6% or more, and (4) single yarn fineness of 2 to 4 denier, (5) total fineness, 1000-2000 denier, (6) 1-4% shrinkage.

In addition, the drawn yarn produced according to the present invention can be converted into a treatment code by a conventional treatment method.

For example, two cords of 1,500 denier drawn yarns are plyed & cabling to 390 tpm (twist / m) (typical polyethylene-2,6-naphthalate treated cord twists) to prepare cord yarns. After immersion in adhesive liquid RFL (Resorcynol- Formalin- Latex) in a first dipping tank, and then in a drying zone at 130-160 ° C under a stretch of 1.0-4.0% under a stretch of 1.0-4.0%. Dry for 200 seconds, heat set for 45 to 80 seconds with a stretch of 2.0 to 6.0% at a temperature of 235 to 245 ° C in a hot stretching zone, and then use a second dipping tank (2nd Dipping tank was again immersed in the adhesive liquid (RFL) and dried for 90 to 120 seconds at a temperature of 140 to 160 ℃, then for 45 to 80 seconds with a temperature of 235 to 245 ℃ and -4.0 to 2.0% stretch Heat-set (Heat Set) to produce a dipped cord (dipped cord).

The deep cord thus prepared (based on 1,500 denier 2-strand top and bottom 390tpm) has a strong utilization of 80% or more and an adhesive strength of 10 kg or more.

As such, the treatment cord made of high modulus and low shrinkage polyethylene-2,6-naphthalate multifilament yarn according to the present invention has excellent dimensional stability and strength, and thus is used as a reinforcement material for rubber products such as tires and industrial belts or other industrial purposes. It can be usefully used for the purpose.

Hereinafter, the present invention will be described in more detail based on the following examples. However, the following examples are not intended to limit the present invention, but are not limited thereto. Various physical property evaluations of the yarns and treatment cords prepared in Examples and Comparative Examples of the present invention were performed by the following methods.

(1) Intrinsic viscosity (I.V.)

After dissolving 0.1 g of the sample in a reagent (90 ° C.) mixed with phenol and 1,1,2,3-tetrachloroethanol at a weight ratio of 6: 4 for 90 minutes to give a concentration of 0.4g / 100ml, Ubbelohde Transfer to a viscometer was carried out for 30 minutes in a 30 degreeC thermostat, and the drop number of seconds of the solution was calculated | required using a viscometer and an aspirator. The number of falling seconds of the solvent was also determined in the same manner, and then the R.V.value and the I.V.value were calculated by the following equation.

Where C represents the concentration of the sample in solution (g / 100ml).

(2) strength

Using Instron 5565 (manufactured by Instron, USA), 250 mm sample length, 300 mm / min tensile speed and 20 turns / s under standard conditions (20 ° C., 65% relative humidity) according to ASTM D 885 Elongation was measured under conditions of m.

(3) shrinkage

The sample was left at 20 ° C. and 65% relative humidity for at least 24 hours, and then weighed at 0.05 g / d to measure the length (L 0), and then dried at 150 ° C. for 30 minutes using a dry oven under no tension. After the treatment was taken out and left for 4 hours or more, the load (L) was measured, and the shrinkage ratio was calculated by the following equation.

(4) Intermediate Shinto

On the S-S curve, the yarn was elongated at 4.5 g / d and the treated cord was elongated at 2.25 g / d.

(5) birefringence

Measurement is made using a polarizing microscope equipped with a Berek compensator.

      (6) adhesion

H-test was performed to measure the initial adhesion to the rubber of the hybrid dip cord. H-test measures the maximum load that the rubber-cord separation occurs by pulling both rubbers while keeping both ends of the deep cord embedded in 9.5mm rubber lumps and keeping the distance between the rubber lumps at both ends 9mm. It is a method of evaluating adhesive force. In addition, sufficient strength is given to a rubber | gum by measuring at 20 degreeC and the pressure of 25 kg / cm <^2> for 20 minutes, before adhesive force evaluation. The rubber composition used in the test was 100 parts of natural rubber, 3 parts of zinc oxide, 28.9 parts of carbon black, 2 parts of stearic acid, 7.0 parts of pintar, 1.25 parts of MBTS, 3 parts of sulfur, 0.15 parts of diphenyl guanidine and phenylbeta naphthylamine 1.0 part is mix | blended.

(7) strong utilization rate

Two strands of filament yarn (A, B) for the strength of the filament yarn measured at 250 mm and the tensile speed of 300 m / min using an Instron low speed tensile tester under standard conditions (20 ° C, 65% relative humidity). ) Shows the percentage of deep cord strength obtained by impregnation after burning.

Strength utilization (%) = Deep code strength / (A yarn strength + B yarn strength) × 100

      Example 1

A solid-state polymerized polyethylene-2,6-naphthalate chip having an intrinsic viscosity (I.V.) of 0.903 and a moisture content of 20 ppm containing 220 ppm of antimony metal was prepared. The produced chips were melt spun using an extruder at a discharge rate of 900 g / min and a spinning draft ratio of 410 at a temperature of 314 ° C. Subsequently, the discharged yarn is solidified through a 60 mm long heating zone (atmosphere temperature 350 ° C.) and a 500 mm long cooling zone (20 ° C., cooling air blowing with a wind speed of 0.5 m / sec), followed by oiling with a spinning emulsion. It was. The partial orientation yarn (POY) is wound at a spinning speed of 2650 m / min, the first stage stretching is 1.4 times at 160 ° C., the second stage stretching is 1.2 times at 170 ° C., and the third stage stretching is 1.3 times at 170 ° C. The final stretched yarn (yarn) of 1500 d / 500f was prepared by performing heat setting at 230 ° C., 2% relaxation, and winding.

After two strands of yarn were rolled up and down at 390 turns / m to prepare cord yarns, the cord yarns were immersed in the adhesive solution of (PCP resin + RFL) in a dipping tank and then stretched 1.0% to 170 ° C in a dry area. After being dried for 150 seconds and heat-fixed at 240 ° C. for 150 seconds in a high temperature stretching area, it was again immersed in RFL, dried at 170 ° C. for 100 seconds, and heat-set at 240 ° C. under -1% stretching for 40 seconds to prepare a treatment cord.

The physical properties of the drawn yarn and the treated cord thus prepared are shown in Table 2 below.

[Examples 2 to 5 and Comparative Examples 1 to 4]

The stretch yarn and the treatment cord were prepared by performing experiments in the same manner as in Example 1 while changing the single yarn fineness of the partial alignment yarn (POY) as shown in Table 1 below.

The physical properties of the drawn yarn and the treated cord thus prepared are shown in Table 2 below.

TABLE 1

division Spinning temperature (℃) Chip specific viscosity Cooling zone Heating zone Partial Aligner (POY) Wind speed (m / sec) Temperature (℃) Length (cm) Temperature (℃) Birefringence Single yarn fineness (denier) Elongation at 0.5 g / d Initial Load (%) Thread 1 314 0.93 0.6 20 40 350 0.065 6.4 4.0 Thread 2 314 0.93 0.6 20 40 350 0.063 8.6 4.6 Thread 3 314 0.93 0.6 20 40 350 0.068 4.3 3.6 Rain 1 314 0.93 0.6 20 40 350 0.059 12.8 5.2 B2 314 0.93 0.6 20 40 350 0.057 17.2 5.7 Rain 3 314 0.93 0.6 20 40 350 0.071 2.1 3.2

TABLE 2

division Drawing company Processing code Remarks Intrinsic viscosity Birefringence Strength (g / d) Elongation (%) Fineness (denier) Single yarn fineness (denier) Shrinkage (%) Strong (kg) Intermediate Elongation (%) Shrinkage (%) Strong utilization rate (%) Adhesive force (kg) Thread 1 0.76 0.432 9.1 9.5 1500 3 1.5 23.5 2.1 1.2 86 14.6 Thread 2 0.75 0.433 8.7 9.8 1500 4 1.6 21.7 2.1 1.3 83 13.5 Thread 3 0.75 0.434 9.3 9.1 1500 2 1.6 23.7 2.1 1.5 85 15.2 Rain 1 0.72 0.424 7.9 9.9 1500 6 1.5 18.7 2.4 1.2 79 9.7 B2 0.75 0.430 7.3 10.1 1500 8 1.5 16.6 2.6 1.3 76 8.8 Rain 3 0.73 0.426 8.3 8.5 1500 One 3.0 19.4 2.5 1.3 78 15.8 ■

■: No appearance of the treatment code due to poor appearance.

The present invention provides a high strength polyethylene having excellent physical properties by maximizing the formation of tie chains connecting the crystals with the orientation and crystals of the partial alignment yarns (POY). Provided are -2,6-naphthalate fibers and a method for preparing the same. In addition, the industrial yarn manufactured according to the present invention provides a treated cord having a strong utilization rate and adhesive strength, and has a high spinning speed, which is advantageous in terms of productivity due to high productivity.

While the invention has been described in detail only with respect to the described embodiments, it will be apparent to those skilled in the art that various modifications and variations are possible within the spirit of the invention, and such modifications and variations belong to the appended claims. .

1 is a process schematic diagram illustrating a fiber spinning process of the present invention.

2 is an example of the force-strain curve of the partial alignment yarn (POY) of the present invention.

Claims (9)

(A) extruding a polymer containing not less than 85 mol% of ethylene naphthalate units and having an intrinsic viscosity in the range of 0.80 to 1.2 at a temperature of 290 to 330 ° C., and passing the molten yarn through a delayed cooling zone and then rapidly quenching , (B) At room temperature, the partial alignment yarn has a single strain fineness of 4 to 10 deniers and a force strain curve that extends less than 5% when subjected to an initial stress of 0.5 g / d, and has an initial modulus and birefringence of 10 to 50 g / d. Winding the yarn at a radial velocity such that 0.02 to 0.20, (C) Polyethylene naphthalate fibers having the following physical properties, prepared by the method comprising the step of multi-stretching the wound yarn to a total draw ratio of 2.5 times or less. (1) intrinsic viscosity of 0.6 to 1.0, (2) strength of 8.0 g / d or more, (3) elongation of 6% or more, (4) 2 to 4 denier of single yarn fineness, (5) 1000 to 2000 denier of total fineness, (6) shrinkage of 1-3% The method of claim 1, Polyethylene naphthalate fiber characterized in that the total fineness of the drawn yarn is 1500 denier, the number of filaments is 500. The method of claim 1, Polyethylene naphthalate fiber characterized in that the total fineness of the drawn yarn is 1500 denier, the number of filaments is 385. The method of claim 1, Polyethylene naphthalate fiber, characterized in that the spinning speed in the step (B) is 2,000 to 3,500 m / min. The method of claim 1, Polyethylene naphthalate fiber produced by the method characterized in that the heating zone of the ambient temperature is 300 to 400 ℃ and the length of 200 to 700mm adjacent to immediately before the cooling zone in step (A). A deep cord obtained by treating two strands of polyethylene naphthalate fibers of claim 1 up and down and treating with resorcinol-formalin-latex (RFL). The method of claim 6, Deep code, characterized in that the strong utilization of the deep code is more than 80%. The method of claim 6, The deep cord, characterized in that the adhesive strength of the deep cord is 10kg or more. A rubber product in which the treatment cord of claims 6 to 8 is incorporated as a reinforcing material.